Genetic clonal diversity predicts progression to esophageal adenocarcinoma.

Neoplasms are thought to progress to cancer through genetic instability generating cellular diversity and clonal expansions driven by selection for mutations in cancer genes. Despite advances in the study of molecular biology of cancer genes, relatively little is known about evolutionary mechanisms that drive neoplastic progression. It is unknown, for example, which may be more predictive of future progression of a neoplasm: genetic homogenization of the neoplasm, possibly caused by a clonal expansion, or the accumulation of clonal diversity. Here, in a prospective study, we show that clonal diversity measures adapted from ecology and evolution can predict progression to adenocarcinoma in the premalignant condition known as Barrett's esophagus, even when controlling for established genetic risk factors, including lesions in TP53 (p53; ref. 6) and ploidy abnormalities. Progression to cancer through accumulation of clonal diversity, on which natural selection acts, may be a fundamental principle of neoplasia with important clinical implications.

Genetic mechanisms of TP53 loss of heterozygosity in Barrett's esophagus: implications for biomarker validation.

BACKGROUND AND AIMS: 17p (TP53) loss of heterozygosity (LOH) has been reported to be predictive of progression from Barrett's esophagus to esophageal adenocarcinoma, but the mechanism by which TP53 LOH develops is unknown. It could be (a) DNA deletion, (b) LOH without copy number change, or (c) tetraploidy followed by genetic loss. If an alternative biomarker assay, such as fluorescence in situ hybridization (FISH), provided equivalent results, then translation to the clinic might be accelerated, because LOH genotyping is presently limited to research centers. METHODS: We evaluated mechanisms of TP53 LOH to determine if FISH and TP53 LOH provided equivalent results on the same flow-sorted samples (n = 43) representing established stages of clonal progression (diploid, diploid with TP53 LOH, aneuploid) in 19 esophagectomy specimens. RESULTS: LOH developed by all three mechanisms: 32% had DNA deletions, 32% had no copy number change, and 37% had FISH patterns consistent with a tetraploid intermediate followed by genetic loss. Thus, FISH and LOH are not equivalent (P < 0.000001). CONCLUSIONS: LOH develops by multiple chromosome mechanisms in Barrett's esophagus, all of which can be detected by genotyping. FISH cannot detect LOH without copy number change, and dual-probe FISH is required to detect the complex genetic changes associated with a tetraploid intermediate. Alternative biomarker assay development should be guided by appreciation and evaluation of the biological mechanisms generating the biomarker abnormality to detect potential sources of discordance. FISH will require validation in adequately powered longitudinal studies before implementation as a clinical diagnostic for esophageal adenocarcinoma risk prediction.

Mucin core polypeptide expression in the progression of neoplasia in Barrett's esophagus.

We have previously demonstrated a specific pattern of mucin (MUC) core polypeptide expression in Barrett's esophagus (BE) characterized by MUC1 and MUC6 positivity in goblet cells in a proportion of cases. The aim of this study was to determine the pattern of MUC expression associated with the development and progression of dysplasia in BE. Endoscopic mucosal biopsies from 35 patients with BE (10 with no dysplasia, 6 with indefinite for dysplasia, 12 with low-grade dysplasia [LGD], and 7 biopsies with high-grade dysplasia [HGD]) were immunostained (ABC method) with antibodies against MUC1, MUC2, MUC3, MUC5AC, and MUC6. The extent and pattern of staining for each marker was evaluated in intestinalized Barrett's epithelium and in the various grades of dysplasia. For cases with dysplasia, staining was evaluated separately in nondysplastic epithelium adjacent to (<1 cm) and distant from (>2 cm) areas of dysplasia. In nondysplastic BE, MUC1, MUC2, MUC3, MUC5AC, and MUC6 stained 40%, 100%, 100%, 100%, and 90% of cases, respectively, in goblet or nongoblet columnar epithelium. With the progression of dysplasia (from metaplasia to indefinite, LGD and HGD), there was a significant decrease in expression of MUC1, MUC2, and MUC3, and alterations in the staining patterns of MUC5 and MUC6. In fact, MUC1 and MUC3 were entirely absent from all cases of HGD. Interestingly, BE-associated adenocarcinomas showed an MUC phenotype distinct from that of HGD, with expression of MUC1 and MUC3 in 47% and 67% of cases, and expression of MUC1 in a membranous pattern. There was no significant difference in MUC staining in nondysplastic BE between patients with and without dysplasia. Alterations in MUC expression occur in the progression of dysplasia in BE. However, none of these markers helps identify a subgroup of patients at increased risk for neoplasia.